Brummel
372eae9cac
Cycle 2 of the "Cost-model graph (in R)" milestone (#148): the milestone's real architectural claim — the cost graph composes. Two pieces: - VolSlippageCost (aura-std): a second, state-dependent cost node whose per-trade charge scales with a measured volatility input (k * vol / |entry - stop|), distinct from ConstantCost's flat charge. The vol is an independent short-horizon realized range, deliberately NOT the stop's own vol — scaling slippage by the vol the stop already normalizes would collapse cost-in-R to a constant (indistinguishable from ConstantCost). - CostSum (aura-std): the cost-graph output node — sums N cost nodes' 3-field cost-in-R records per-field into one aggregate record. So summarize_r and the net_r_equity LinComb(4) read the AGGREGATE and stay structurally unchanged (one home for cost; n=1 is the identity, keeping the cost path uniform). Run-path wiring: --cost-per-trade and --slip-vol-mult combine, their costs summing into the net-R curve; a hoisted vol proxy keeps the single-feed pattern. A no-cost run stays byte-identical (C18 golden floor). Scope is the run path; sweep/walkforward/mc still pass None (sweep-path cost remains deferred), and the general CostNode trait stays deferred (designed against two shipped nodes later). Auto-signed under /boss on the grounding-check PASS: all 8 load-bearing existing-behaviour assumptions tie to named green tests. Fork decisions recorded on #148. refs #148